Re: another brain teaser for the math inclined
Hint: The problem becomes much easier if you don't leave out kid #2. I'm assuming kid #2 got lost in translation somewhere.
Answer in white: <font color="white"> Only perfect squares will be open, i.e 2, 4, 12, 16, 25, 36, 49, 64. If kid #2 was supposed to be left out, just take my answer and switch all the even doors.</font>
Reasoning: <font color="white"> Only perfect squares have an odd number of factors </font>
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